Compound semiconductors are widely used in the electronic industry and are important compound semiconductor materials, such as InP, GaP, and GaAs. Due to the presence of volatile elements, the synthesis of these compounds is very difficult. Commonly used synthesis methods include horizontal diffusion synthesis and injection synthesis. Crystal growth methods include liquid encapsulated czochralski (LEC) method and vertical gradient freezing (VGF) method. Since the LEC method requires high equipment cost, large crystal stress, high dislocation density, complex crystal growth process, and is not conducive to the growth of high-quality large-size single crystals, the VGF method is widely used currently.
Bell Labs first used the VGF method to prepare III-V compounds in the 1980s. This method is a crystal growth method in which a container filled with indium phosphide polycrystalline raw materials is vertically placed at a corresponding temperature gradient position set in a furnace, red phosphorus is distributed around the container, and after the polycrystalline raw materials are completely molten, crystallization slowly starts from one end at a lower part all the way to one end at an upper part. The VGF method has a slow growth speed and a small temperature gradient, so crystals are less stressed, as a result, crystal materials with relatively low dislocation density can be grown. However, in this method, a seed crystal needs to be placed in a crucible before crystal growth. It is difficult to realize continuous VGF crystal growth after synthesis, because it requires direct contact between the seed crystal and pure metal. In a high-temperature pure metal melt, the compound seed crystal will be molten or eroded by the pure metal or the melt being synthesized. In order to protect the seed crystal, it is necessary to put polycrystalline raw materials into the crucible in advance and protect the seed crystal from being molten in a synthesis process through complicated temperature control procedures. However, this will lead to a reduction in the purity of a synthesized crystal material, and make the growth process of synthesized crystals time-consuming, complicated and error-prone, and make industrialization and large-scale growth difficult, which seriously hinder the application and development of semiconductor crystal materials.